In a cellular system, for initial synchronization, a terminal should acquire timing synchronization and frequency synchronization on the basis of signals transmitted from a base station, and perform a cell search. After the initial synchronization, the terminal should track the timing and frequency, and perform the timing and frequency synchronization between adjacent cells and the cell search in order for handover.
In a synchronous cellular system, all base stations can perform frame synchronization using common time information from an external system. However, a cellular system that has been developed by 3GPP (3rd generation partnership project) is an asynchronous system in which the frame timings of all base stations are independent. The asynchronous cellular system needs to perform a cell search process, unlike the synchronous cellular system.
Therefore, a method of acquiring synchronization using a separate preamble and searching a cell has been proposed. However, the method cannot be applied to a system without the preamble. In addition, a method of acquiring synchronization and searching a cell using pilot symbols disposed at start and end points of a sub-frame has been proposed. However, the method has a problem in that a large number of pilots should be used.